Final answer:
It is unnecessary to add adenosine residues in vitro to mRNA for sequencing because the RNA is already mature and contains any necessary modifications. Splicing and RNA editing are important for the diversity of proteins and might reflect ancient RNA-based life forms' biochemical processes.
Step-by-step explanation:
When isolating messenger RNA (mRNA) for sequencing, one might notice that the length of mRNA is shorter than its corresponding DNA sequence. This is because mRNA undergoes post-transcriptional modifications like splicing, where introns are removed while only exons are expressed in the final mRNA. Splicing allows for alternative gene splicing, which offers evolutionary advantages by increasing the diversity of proteins an organism can produce from a single gene.
In vitro mRNA sequencing typically does not require the addition of adenosine residues because the RNA sequence to be analyzed is already in its mature form without introns and with necessary modifications such as a 5' cap and a poly-A tail, if these are present in the species being studied. The technique of RNA sequencing relies on technology that reads the existing sequence without the need for additional adenosine residues. RNA editing is another fascinating aspect where RNA molecules, instead of proteins, can serve as catalysts in gene expression regulation, as observed in the mitochondria of some plants and animals. This might be a relic of ancient RNA-based life forms, suggesting that RNA molecules once had a larger role in biochemical reactions than they do in most modern biology. One example of RNA editing is the insertion of uracil residues in place of adenine in guide RNA's interactions during RNA editing.